Many different devices and/or structures, such as an aileron of an airplane wing, a flap on the trailing edge of an airplane wing, and a boat hull, include components manufactured with composite materials. One of the many reasons for this is that the components may be easily contoured into complex curves, like those found in a hull or leading edge of a flap, during the manufacture of the components. Another reason is that the components may be easily repaired in the field, and thus, the time spent completing a repair may be reduced.
Repairing a component with composite materials typically involves laying up two or more plies of material such as metal, woven and/or non-woven carbon, fiberglass, and/or Kevlar® fibers with an adhesive and then curing the adhesive to couple the two or more plies together and to couple the plies with the remainder of the component. To provide a strong repair, the adhesive should be properly cured; otherwise the repair and/or component could prematurely fail. Properly curing most conventional adhesives includes three elements: heating the adhesive, exerting pressure on the repair—typically about 200 psi—, and applying a vacuum to the repair. Heating the adhesive changes the adhesive's molecular structure to solidify and increase the material strength of the adhesive. Exerting pressure on the repair compacts the plies to increase the strength of the interlaminate bonds and increase the distribution of adhesive throughout the repair. And applying a vacuum draws out gas that would otherwise be trapped in the repair once the adhesive solidifies to reduce the number and size of voids in the cured adhesive. Although most conventional adhesives may be cured under a variety of different pressures, in general, as the pressure increases the strength of the repair increases.
Unfortunately, properly curing a repair to a component in the field is difficult because the amount of pressure that may be exerted on the repair is typically equal to or less than 14.7 psi. To cure a repair in the field, a heating blanket is typically placed on the repair, and then a bag is placed over the entire repair and sealed to the component. The air between the bag and the repair is then removed to generate a vacuum and the heating blanket is turned on to generate heat. Thus, the only pressure that is typically exerted on the repair is atmospheric pressure that results from the vacuum, which is about 14.7 psi.
A possible solution is to design a component that will withstand the stresses and strains encountered in service with a repair that does not contribute to the component's structural integrity. But this means that the component, when manufactured, will be more robust than is required. Consequently, the cost in material to manufacture the component and the weight of the component will be more than required to meet the expected stresses and strains encountered in service. This increase in cost and especially weight can be significant, for example, in an airplane predominately made of composite materials.
Another possible solution is to cure the repair in an autoclave, which is typically used to cure components during their manufacture. But using an autoclave in the field is often impractical because of its size. Most conventional autoclaves are expensive to build, and thus expensive to purchase, because they are designed to perform many complimentary curing functions. For example, most autoclaves are designed to pressurize an internal chamber to about 200 psi, and thus, specifically designed to withstand this pressure. Furthermore, most autoclaves include a pump or compressor to generate this pressure, a heater to heat the atmosphere, a fan to circulate the heated atmosphere, and a system to purge gases from the atmosphere, which may be released into the chamber as the adhesive cures. Consequently, most autoclaves are large to accommodate a wide range of component sizes.
The size of most autoclaves makes their use in the field impractical for many reasons. One reason is that large autoclaves are difficult to move from one location in the field to another. Another reason is that large autoclaves are expensive to operate because the volume of air that must be heated and circulated within the autoclave to cure a component and/or repair to a component is large. Consequently, about the same amount of power is required to cure a repair to a small component as a repair to a large component.